In Wide-band Code Division Multiple Access (WCDMA) and Long Term Evolution (LIE) systems, discontinuous reception (DRX) allows the user equipment (UE) to switch off its radio receiver and thereby drastically reduce its power consumption in idle mode or in other low activity modes. The low RRC activity mode in WCDMA includes Cell_PCH state, URA_PCH state and it can also include the Cell_FACH state. For instance, in WCDMA, when the UE is idle or is in the Cell_PCH or URA_PCH states, it can reduce its power consumption from 100-400 mA down to 5-10 mA using DRX. In the later release of WCDMA (release 7) the UE can also make use of DRX in connected mode to save its battery consumption. In LTE the same DRX cycles will be applicable in both idle and connected modes. This will allow considerable saving of the UE battery consumption.
A UE, once registered to the network is allocated a Paging Group (PG). For the PG, there are paging indicators (PIs) which appear periodically on the Paging Indicator Channel (PICH) that indicates when there are paging messages to any of the UEs belonging to that PG. Thus, when the UE is idle, its main task is to monitor the PICH periodically to receive information when the UE is being paged. That is performed by monitoring the PI:s for its associated PG. As stated above, the PI:s are carried on the PICH and the PI:s inform the different UEs about the instant when they should decode the information of the PCH channel. If the UE detects that its PI has been set, it listens to the paging channel (PCH) in the subsequent PCH frame. During those periods when it is not required to monitor the PICH, the UE typically conserves power by powering off its receiver. The time between the transmissions of successive PI:s for a given UE is the DRX cycle length. Because the UE's power consumption is less when its receiver is switched off than when it is on, the UE's power consumption and thereby its idle time is largely determined by the DRX cycle length.
The UE must be able to receive the paging information in the whole cell area. The less often the UE has to tune the receiver to listen for a possible paging message, the longer the terminal's battery will last in idle mode. The paging procedure is schematically illustrated in FIG. 1. An application 14 transmits a paging message 15 to the UE via the RNC 12 and the radio base station 11. A radio connection is set up 17 by means of a RRC connection request to allow the UE to respond to the paging message by sending a paging response 18.
When the UE is in idle mode, the UE also performs measurements in order to continuously camp on the best cell in terms of the received power and signal quality (measured on the common pilot channel or on reference symbols). In order for the UE to perform the necessary measurements, it needs to switch on its radio receiver to collect several measurement samples of the received pilot or reference symbol strength and/or quality. Furthermore, these measurements are done for several cells, which may also belong to different access technologies, as dictated by the neighbor cell lists. The UE evaluates the cell reselection criteria (as defined in TS 25.304: User Equipment (UE) procedures in idle mode and procedures for cell reselection in connected mode) at least once in every DRX cycle. If the UE is on the move, cell reselection related measurements and the corresponding evaluation must be made sufficiently frequently in order to be able to camp on the best cell.
Thus, the length of the DRX cycle represents a trade-off between the power consumption in certain UE modes (notably in idle mode) on the one hand and the paging response time and the accuracy of the cell reselection process on the other. Allowable DRX cycles are specified to address this trade-off in 3GPP TS 25.331. “Radio Resource Control Specification”.
Subscribers are often stationary for a longer period of time. For instance, a large group of mobile subscribers stay in the office or at home for a long period as compared to the typical DRX cycle discussed above. In addition, in some situations, a subscriber may want to block incoming sessions including voice calls and other real time (e.g. video) sessions. Indeed, blocking of incoming calls is a common and well known service provided by, for instance the Session Initiation Protocol (SIP), further described in “SIP Silent Rejection Service”, available at: http://www.sipcenter.com/sip.nsf/html/SIP+Silent+Rejection+Ser vice. Incoming call blocking is particularly useful for mobile phones that are often used as pocket calculators, digital cameras, music recording devices, i.e. for various non-network related services.
The existing technology described in TS 25.304 “User Equipment (UE) procedures in idle mode and procedures for cell reselection in connected mode” and TS 25.133 “Requirements for support of radio resource management (FDD)” facilitates power saving by allowing the UE to employ discontinuous reception. The elapsed time between successive measurements however is too conservative relative to the measurement period that is necessary in certain scenarios such as for large user group's typical or recurring scenarios. Therefore, the UE power consumption in this type of scenarios is higher than necessary.
This problem is recognized by the 3GPP in TS 25.133 “Requirements for support of radio resource management (FDD)”, and therefore the DRX cycle length can be dynamically set. However, the fundamental trade-off between the DRX cycle length, the cell reselection process and the paging response time does not allow the DRX time to be set too high. This is because in the current design the UE keeps monitoring the PICH even when the subscriber (and, in effect, the UE) does not want to receive incoming calls and/or session initiations. Thereby, reducing the UE power consumption below the typical 5-10 mA is not possible with existing solutions.